URBAN METABOLISM FOR RESOURCE-EFFICIENT CITIES

While the theoretical potential of the urban metabolism concept to support urban planning and design forresource efficiency is supported in scientific literature (e.g. Kennedy et al., 2011, Pincetl et al., 2012,Beloin-Saint-Pierre et al., 2016), its practical implementation is so far limited (Voskamp et al., In Press). Thisraises questions about the value of the concept of urban metabolism in understanding urban processes tosupport resource-efficiency interventions; and how it can transition from theory to practical implementationwhen quantitative assessments are considered. To explore these questions, this report begins by criticallyreviewing the concept of urban metabolism in the context of resource-efficient cities. Further, it reviewsapproaches to urban metabolism assessment and their application in urban contexts. Finally, based on criticalliterature analysis, the report provides perspectives for transitioning from theory to practical implementation.2. The concept of urban metabolism2.1 DefinitionThe concept of urban metabolism has re-emerged after being overlooked for many years (Barles, 2010). Interestingly, there is no consensus in the literature on the foundations of the concept. For instance, Kennedy et al.(2011) highlight Abel Wolman (1965) as the founder of the concept, when he examined the process of supplyingmaterial, energy and food to a hypothetical city, as well as its respective output products. Lin et al. (2012) arguethat Burgess (1925), a sociologist, first utilised the term with no formal definition to analogise urban growth tothe anabolic and catabolic processes. Barles (2010) suggests the concept was not formulated for the urbancontext in the 19th century, but used by chemists who were concerned with wastewater and fertilizer use inagriculture production. Others trace the term to Marx in 1883 when he described the exchange of materials andenergy between society and environment (Pincetl et al., 2012, Zhang, 2013). Recently, Lederer and Kral (2015)have evidenced Theodor Weyl, a German chemist and medical doctor, as the founder of current urban metabolism studies. His 1894 publication, ‘Essays on the metabolism of Berlin,’ investigated nutrient flows dischargedfrom Berlin, comparing them to nutrient consumption through food intake.The urban metabolism can be understood as the process by which a city attains resources from its local environmental hinterland or through trade, consumes them for the production of economic outputs and social services(which are ideally, but not actually, equitably distributed), and releasesthe wastes into the environment. Kennedy et al. (2007) define the urbanUrban metabolism can bemetabolism as the ‘sum of the technical and socio–economic processunderstood as the “collection es that occur within the cities, resulting in growth, production of energy,and elimination of waste’. Although other studies provide the conceptof complex sociotechnicaldefinition (e.g. Wolman, 1965, Graedel, 1999, Baccini and Brunner,and socio-ecological2012), Kennedy and colleagues’ definition is the most cited in the literaprocesses by which flows ofture. Their definition explicitly encompasses essential components of anurban system but with a specific bias towards industrial ecology, whichmaterials, energy, people,focuses on quantification, and excludes the emergent urban activitiesand information shape themade possible through resource exchange. Recognising it as wider thancity, service the needs of itsindustrial ecology, the urban metabolism can be understood as the“collection of complex sociotechnical and socio-ecological processes bypopulace, and impact thewhich flows of materials, energy, people, and information shape the city,surrounding hinterland.”service the needs of its populace, and impact the surrounding hinterland” (Currie and Musango, 2016). Ferrao and Fernandez present theseprocesses in an urban metabolism assessment framework (Figure 2), which connects resources, urban bio-social processes, and the urban activities of providing housing, goods and services, and transporting people andgoods.The discrepancies in the apparent foundations of the concept of urban metabolism indicate that a singledisciplinary enquiry is not sufficient. This is evidenced by calls to integrate the concept so as to better understandthe socio-technical and socio-ecological process of urban systems. This demands transdisciplinary actions (Linet al., 2012), in which researchers move between disciplines but also engage directly with stakeholders. MorePage 4Urban Metabolism For Resource-efficient Cities: From Theory To Implementation

urban economyinputspassiveflora faunabiogeochemical contextcarbonwaternitrogenairphossolar icipalhidden flowspassiveexportsactivesocioeconomic contextwaterenergyUA2B. Env. & InfrastcmaterialsairheatUA3Goods & unicipalsinkregionalhidden flowsexportedmun.wastebiomassregionalhidden flowsenvironmental dispersion(heat, materials, air water)Figure 2: Urban metabolism framework. Source: Ferrao & Fernandez (2013:40)so, the formal definitions should not only integrate flows of natural, industrial and urban materials and energy,but also flows of people and information (Currie and Musango, 2016). Finally, the urban metabolism is hugelyshaped by political context, which influences the political commitment to translate knowledge into practicalimplementation. Guibrunet et al. (2016) suggest that the urban metabolism concept offers an importantperspective for drawing out the political realities of a city.Castán Broto (2012) highlights six themes that emerged within interdisciplinary boundaries in relation to theurban metabolism: “(i) the city as an ecosystem; (ii) material and energy flows within the city; (iii) economic–material relations within the city; (iv) economic drivers of rural–urban relationships; (v) reproduction of urbaninequality; and (vi) attempts to re-signify the city through new visions of socio-ecological relationships”.2.2 Motivating the use of urban metabolism assessmentBarles (2010) provides two perspectives for urban metabolism studies. The first is applied research and decisionsupport, which examines: (i) urban biogeochemistry processes; (ii) implications of the material and energy needsof cities on other spaces and the entire biosphere; (iii) biogeochemical and social operations interactions. Thesecond is a tool to address sustainable development challenges and the requirements to achieve dematerialisation1, decarbonisation2 and the closing of material loops. These studies entail constructing indicators, identifyingsustainability targets and developing decision support tools for strategies to dematerialise or decarbonise. Thisreport concentrates on the second perspective, with the specific aim to shift from theory to implementation ofresource efficiency plans and designs.12The consumption of fewer materialsThe consumption of less carbonPage 5Urban Metabolism For Resource-efficient Cities: From Theory To Implementation

The increasingly widespread use of urban metabolism assessments is driven by a need to radically decrease theresources required to enable economic growth and a good quality of life. This need is motivated by the UNEnvironment Report, Decoupling natural resource use and environmental impacts from economic growth (UNEP,2011) which calls for a decoupling of economic production from resource consumptionas well as from environmental degradation. It presents a number of scenarios for a safe It is importantlevel of global resource consumption, most notably a scenario in which countries of the to promoteglobal North reduce consumption while countries of the global South increase consumpimproved accesstion (which is required as many of these populations lack access to basic resources),converging at a global level of 70 billion tons of materials consumed in 2050. This to resources in aamounts to about 8 tons per person, which is about a third of the United States’ resource-efficientconsumption, half of typical current European consumption, and double the averagemanner.African country’s consumption. As cities are the concentrators of resource consumption,it is imperative that they lead the shift towards this goal of 8 tons per capita, through resource-efficiencymeasures. It is important to be aware of the misconception that many cities of the global South appear to beresource efficient already, as this is largely due to unmet demands that have serious negative consequences forthe poor. In these contexts, it is important to promote improved access to resources in a resource-efficientmanner so that the benefits can be shared by more people.2.3 The city: from organism to ecosystemAn urban metabolism perspective on cities also differs based on the central metaphor utilised: ‘organism’ or‘ecosystem’. As organisms, cities are seen to share attributes with organisms in their distribution resourcesthrough networks: cities are likened to a human body (Golubiewski, 2012). For instance, similar to blood vesselsor the vascular networks which distribute energy and materials to cells in an organism, city networks ofinfrastructure (e.g. power lines or roads) distribute energy, materials and people throughout an urban area. Theperspective of cities as ecosystems only became common in the second half of the 20th century (UNU-IAS UrbanEcosystems Management Group., 2003).Odum (1971; 1973) proposed that materials and energy in societies can be analysed in the same manner as fororganisms and ecosystems. While the approach for cities as organisms is not entirely new, the notion that toolsfrom biology can be used to study cities is increasingly relevant for ecologists studying the metabolism of cities(Decker et al., 2000; 2007), the ecological footprints of cities and regions (Luck et al., 2001), and the ecologicalimpacts of human societies (Vitousek et al, 1997; Wackernagel et al., 2002; Bettencourt et al., 2007). Over theyears, the conceptualisation of a city has however taken various paths, which can be categorised as an urbanecology approach, flows approach, or biosocial approach (Table 1).Table 1: Trajectories in conceptualizing a cityCategoryDescriptionUrban ecology approachThis largely remains within the realm of biology. The urban ecologists haveregarded cities as unique typ

which flows of materials, energy, people, and information shape the city, service the needs of its populace, and impact the surrounding hinter-land” (Currie and Musango, 2016). Ferrao and Fernandez present these processes in an urban metabolism assessment framework (Figure 2), which connects resources, urban bio-so-